The present invention relates to a process for hydrocracking coal and other carbonaceous materials. The materials contemplated include anthracite, bituminous and lignite coal, as well as peat, oil shale, tar sand, wood, lignin, solid petroleum residuals and other related materials. The development is particularly applicable to the conversion of lignite and bituminous coal to liquid and gaseous hydrocarbon products.
Hydrocracking or hydropyrolysis is the thermocracking of coal in the presence of hydrogen. Reaction temperatures and pressures are moderately high, from about 1200.degree. to 1800.degree. F. and from 1500 to 2500 psig. When solid coal particles are heated, the volatile matter is released. The initial devolatilization appears to take place in two broad steps. In the first step moisture, carbon oxides, chemically formed water, tars and methane are released from a reactive semi-char. Upon further heating, the semi-char is dehydrogenated to a less reactive char. A large flow of gases from the particles in the initial stages prevents hydrogen from entering the coal particles and diffusing to react with coal hydrocarbons. The materials emitted during coal pyrolysis diffuse into the bulk gas phase where reactions such as tar hydrogenation can take place.
Bitumins and other polynuclear aromatic materials from coal become sticky on heating which can produce the agglomeration of carbonaceous particles in process equipment. This can block or restrict passageways in and near high-temperature components such as the hydropyrolysis reactor and preheater. Also such condensed material may carbonize to form coke on the equipment walls and restrict flow in that manner. Other hydrocracking products including alkylated and hydroxylated aromatics such as xylenes, phenols, creosols and toluenes may be desired in differing proportions depending on the use to be made of the product. For example, high concentrations of benzene, xylene and toluene may be desirable for gasoline feed stock while other aromatics may be preferred for a particular chemical feed stock. Often a balanced blend of various aromatics is sought in the processing of coal and other carbonaceous materials.